Low power methods for signal processing blocks in ethernet phy

ABSTRACT

A method includes receiving an input signal at a filter, where the filter includes a plurality of filter taps, and where each of a first filter tap and a second filter tap has a weighting coefficient. The method also includes shutting down the first filter tap based on the weighting coefficient of the first filter tap being below a threshold and the weighting coefficient of the second filter tap being below the threshold, where the second filter tap is next to the first filter tap.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Indian Provisional PatentApplication No. 202041010814, which was filed Mar. 13, 2020, is titled“Novel Low Power Methods For Signal Processing Blocks In Ethernet PHY,”and is hereby incorporated herein by reference in its entirety.

The present application relates to the commonly-assigned, co-pendingapplication titled “Interleaving ADC Error Correction Methods ForEthernet PHY,” which has Ser. No. ______, a filing date of ______, andan Attorney Docket Number TI-92401, and which claims priority to IndianProvisional Patent Application No. 202041024507, which has a filing dateof Mar. 13, 2020 and is titled “Interleaving ADC Error CorrectionMethods for Ethernet PHY.” Both applications are hereby incorporatedherein by reference in their entireties.

BACKGROUND

Ethernet is a network protocol that controls how data is transmittedover a local area network (LAN). Gigabit Ethernet transmits Ethernetframes at a rate of one gigabit per second. Data is transmitted overshielded or unshielded twisted pair cables. An Ethernet receiverreceives data from a transmitter. The receiver includes an analog frontend followed by a digital processing section.

SUMMARY

In accordance with at least one example of the description, a systemincludes a filter configured to receive an input signal, the filterhaving a first tap, a second tap, and a third tap, and each first tap,second tap, and third tap having a weighting coefficient and a datagate. The data gate is configured to shut down the first filter tapresponsive to the weighting coefficients of the first filter tap, thesecond filter tap, and the third filter tap each being below athreshold, and where the second filter tap and the third filter tap areeach next to the first filter tap.

In accordance with at least one example of the description, a methodincludes receiving an input signal at a filter, where the filterincludes a plurality of filter taps, and where each of a first filtertap and a second filter tap has a weighting coefficient. The method alsoincludes shutting down the first filter tap based on the weightingcoefficient of the first filter tap being below a threshold and theweighting coefficient of the second filter tap being below thethreshold, where the second filter tap is next to the first filter tap.

In accordance with at least one example of the description, a methodincludes determining a mean square error (MSE) for a signal in anEthernet receiver. The method includes comparing the MSE to a targetMSE. The method also includes changing a threshold for shutting down afilter tap responsive to the MSE being above or below the target MSE andan error value. The method includes setting the threshold for shuttingdown the filter tap responsive to the MSE being above the target MSEminus the error value or below the target MSE plus the error value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a receiver in an Ethernet system inaccordance with various examples.

FIG. 2 is a block diagram of an echo canceller in accordance withvarious examples.

FIG. 3 is a graph of echo coefficients for 216 echo canceller taps inaccordance with various examples.

FIG. 4 is a graph of echo canceller taps and echo coefficients inaccordance with various examples.

FIG. 5 is a graph of echo canceller taps and echo coefficients inaccordance with various examples.

FIG. 6 is a table of performance results in accordance with variousexamples.

FIG. 7 is a flow diagram of a state machine that provides asignal-to-noise ratio (SNR) based iterative shutdown method inaccordance with various examples.

FIG. 8 is a graph of echo canceller taps and echo coefficients inaccordance with various examples.

FIG. 9 is a table of performance results for shutting down filter tapsusing the neighbor method in accordance with various examples.

FIG. 10 is a diagram of a channel length-based shutdown method inaccordance with various examples.

FIG. 11 is a flow diagram of a method for reducing power consumption inan Ethernet receiver in accordance with various examples.

DETAILED DESCRIPTION

Some Ethernet applications, such as automotive applications, areemployed in situations where low power consumption is useful. High speedEthernet implementations may consume large amounts of power. Oneconventional technique for reducing power is to share the hardware usedfor filter taps within an echo canceller in the digital section of thereceiver. Another conventional technique for reducing power is to shutdown certain filter taps if those filter tap values are below athreshold. However, these conventional techniques may not reduce powerconsumption to a more useful level, and may cause performance to fallbelow an acceptable threshold.

In examples herein, certain filter taps in an Ethernet receiver may beshut down to reduce power consumption. Unwanted filter taps aredistinguished from wanted filter taps, and the unwanted filter taps maybe shut down. Rather than using an absolute threshold to shut down afilter tap, a filter tap may be shut down if the filter tap and acertain number of neighboring filter taps each have filter tapcoefficients that are lower than a predetermined threshold. In anexample, the predetermined shutdown threshold may be tuned based on atarget signal to noise ratio (SNR). The target SNR may be based on theEthernet channel length in another example. With the use of some or allof these techniques, power consumption may be reduced while stillmaintaining acceptable performance of the system.

Receiver 100 (shown in FIG. 1) may be implemented in an Ethernet systemin accordance with various examples herein. FIG. 1 illustrates theEthernet physical (PHY) layer receive path. The transmitter path is notshown in FIG. 1. Receiver 100 includes an analog front end 102 and adigital signal processing section 104. In operation, an input signal isreceived at receiver input 106 via a network conductor (such as a localarea network cable, an Ethernet cable or some other network connectionor bus). The input signal passes through high pass filter 108 (e.g. ananalog high pass filter). A coarse automatic gain control (CAGC) 110provides gain to the input signal, so the amplitude of the input signalis at an appropriate level for other components in receiver 100. Inaddition, an appropriate gain (with little or no added noise) willincrease the signal-to-noise ratio of the input signal. In anotherexample embodiment, HPF 108 may include a low-noise amplifier (notshown) and a high-pass filter. CAGC 110 is in digital signal processingsection 104 in this example.

High pass filter 108 provides the filtered input signal to programmablegain amplifier (PGA) 112. PGA 112 provides additional amplification tothe input signal. The input signal is then provided to an analog todigital converter (ADC) block, which includes ADC 114A and ADC 114B inthis example (collectively, ADCs 114). In one example, receiver 100 hasa symbol rate of 750 megahertz (MHz). ADCs 114A and 114B areinterleaved, so each ADC 114 operates at 375 MHz to provide a totalthroughput of 750 MHz. The clock signal in this example is provided by a750 MHz phase locked loop (PLL) 116. The clock signal passes through aphase interpolator 118, which may lag or lead the clock signal duringoperation. Phase interpolator 118 has a 6-bit control in one example,which means it may adjust the phase of the clock signal by 2⁶=64different values. A clock recovery loop 120 in digital signal processingsection 104 sends a phase up/down signal to control phase interpolator118.

The clock output from phase interpolator 118 is divided into 375 MHzrecovered clock signals at clock divisor 122. The 375 MHz clock signalsare provided to ADCs 114. A timing recovery loop that includesincremental ADC (iADC) delay control 124 and iADC timing loop 126 (indigital signal processing section 104) provide timing recovery functionsfor ADCs 114A and 114B.

Output signals from ADCs 114A and 114B are provided to FIFO (first infirst out) 128 in digital signal processing section 104. FIFO 128receives the signals from ADCs 114A and 114B and provides multiple paths(for purposes of this description, six paths) at its output. Only asubset of the six paths is shown here. Each of the six paths operates at125 MHz (e.g. determined by 750 MHz divided by the number of paths,which is six in this example), which provides a total operating speed of750 MHz. Each of the six paths includes a gain component 130(collectively, gain components 130). Only three gain components 130A,130B, and 130C are shown for simplicity. The gain of the gain components130 may be adjusted with an iADC gain control signal provided by iADCgain loop 132. The output signals of the gain components 130 areprovided to an echo canceller 134.

Echo refers to interference between transmitted and received data on achannel. Echo may be generated if a near-end transmitted signal isreflected from a transmit path onto a receive path. Echo may also begenerated if at least a portion of a transmitted signal on an individualpair of twisted wire(s) is reflected back from a target device. Echocanceller 134 provides echo cancellation and is described in examplesbelow. In some examples, echo cancellation may be performed in analogfront end 102 as well (not shown in FIG. 1). Echo canceller 134generates an echo estimate and attempts to cancel the echo bysubtracting the echo estimate from the signal. An adaptive filter, suchas a finite impulse response filter, may be used to model the responseof the echo path.

After echo canceller 134 provides echo cancellation, echo canceller 134provides signals on six paths. In this example, six paths are used, butin other examples there may be a different number of paths, or only onepath. The six signals are provided to a fine automatic gain control(FAGC) component 136. Two FAGCs 136A and 136B (collectively, FAGCs 136)are shown for simplicity, rather than all six used in this example.FAGCs 136 provide fine gain control to the signals in conjunction withgain loop 138. The six signals are then provided to digital equalizer(DEQ) 140. DEQ 140 provides equalization to the signals, which are thenprovided to feed forward equalizer (FFE) 142, which also providesequalization to the signals. FFE 142 may use delay components to provideweighted signals that are fed forward and summed to provide equalizationin one example.

At the output of FFE 142, a parallel decision feedback equalizer (DFE)144 receives the output signals and stores symbols in a shift registerwithin DFE 144. DFE 144 uses a feedback loop with adders 146A and 146B(collectively, adders 146; only two adders 146 are shown for simplicity)to remove intersymbol interference (ISI) from the output signals. ISIoccurs if one symbol interferes with another symbol. After DFE 144removes ISI, symbols are sampled by slicers 148A and 148B (collectively,slicers 148; two slicers 148 are shown, although there may be moreslicers 148 in other examples), and then the symbols are provided to thenext processing block of the Ethernet implementation.

A substantial portion of the current in receiver 100 is consumed by echocanceller 134, FFE 142, and DFE 144. Reducing current in thesecomponents may help to reduce the overall current consumed by receiver100. In one example, digital signal processing section 104 consumesapproximately 250 milliamps (mA) of current. DFE 144 consumesapproximately 80 mA, echo canceller 134 consumes approximately 60 mA,and FFE 142 consumes approximately 10 mA. In this example, each of thesecomponents includes a filter that has a plurality of filter taps. DFE144 has 42 filter taps, echo canceller 134 has 216 filter taps, and FFE142 has 4 filter taps. In other examples, these components may havedifferent numbers of filter taps. By shutting down filter taps ifneighboring filter taps are below a certain threshold according toexamples described below, current consumption may be reduced in receiver100. In an example herein, DFE 144, echo canceller 134, and/or FFE 142are configured to shut down filter taps responsive to neighboring filtertaps being below a certain threshold, thereby reducing powerconsumption. These techniques are now described with respect to FIG. 2.

FIG. 2 is an echo canceller 200 in accordance with various examples.Echo canceller 200 is an example implementation of echo canceller 134from FIG. 1. In other examples, echo canceller 200 may include othercomponents not illustrated in FIG. 2. Echo canceller 200 includes a datapath 202 and a least mean square (LMS) block 204. Transmit data 206enters a shift register 208 in echo canceller 200. Transmit data 206 isa transmit signal that interferes with signals on the receive side (suchas receiver 100). In one example, transmit data 206 represents theoriginally transmitted signal that reappears, with some delay, in thereceived signal (e.g., an echo). Once the echo is recognized, it may beremoved by subtracting it from the received signal. A digital signalprocessor, analog circuitry, or software (not shown in FIG. 2) mayrecognize the echo signal and convert it to a digital signal, such astransmit data 206. Echo canceller 200 is configured to cancel thisinterfering transmit data 206. Transmit data 206 is received in the formof symbols 0, 1, or −1 in this example, which are saved in shiftregister 208. In this example, shift register 208 has 216 filter taps209, which makes this a 216-tap filter. Four filter taps 209A to 209Nare shown in FIG. 2 for simplicity. The output of each filter tap 209 ismultiplied by a weighting coefficient (referred to hereinafter ascoefficients) using multipliers 210A to 210N (collectively, multipliers210). The products of multipliers 210 are summed by adder 212. A digitalinput signal 214 is added to the output of adder 212 with adder 216.Digital inputs signal 214 is an input signal from an ADC such as ADC 114(FIG. 1). Digital input signal 214 includes the unwanted echo signal.Digital input signal 214 and adder 216 may operate to cancel therecovered echo signal. The output of adder 216 is provided to equalizer218, which equalizes the signal. The output of equalizer 218 is providedto slicer 220, which produces a slicer output 222.

Coefficients for the echo canceller 200 are found on the right side ofecho canceller 200 using LMS block 204. Slicer error for slicer 220 isfound with adder 224. The slicer error is provided to LMS block 204. Theslicer error is multiplied by the transmit data 206 from the filter tap209 on the shift register 208 for a given filter tap i 209 by usingmultiplier 226. The result of multiplier 226 is scaled down withamplifier 228 and accumulated with adder 230. The result of theaccumulation is stored in register 232. Register 232 contains the echocanceller coefficient, which is estimated during training. Over time, acoefficient 234 is produced by LMS block 204 for a given filter tap i209.

In an example, 216 LMS blocks 204 are used to determine the 216coefficients. To reduce power consumption, an LMS sharing technique isuseful. Rather than 216 separate LMS blocks 204, some of the hardwaremay be shared with more than one coefficient in a time multiplexedmanner. That is, on a first clock cycle, a first coefficient is updatedusing a first LMS block 204. On a second clock cycle, the same first LMSblock 204 updates a second coefficient. The same first LMS block 204 isused on a third clock cycle to update a third coefficient, and usedagain on a fourth clock cycle to update a fourth coefficient. Therefore,each LMS block 204 may be used four times, which is a technique known as4× LMS sharing. With this technique, only 54 LMS blocks 204 are usedrather than 216 LMS blocks 204. In another example, each LMS block 204is used twice, which is called 2× LMS sharing. 4× LMS sharing may saveapproximately 20 mA current consumption in some examples.

Echo canceller 200 may also produce a mean square error (MSE). Theoutput of adder 224 in echo canceller 200 is the slicer 220 error, andprovides an example of noise in the system. MSE may be calculated fromthis noise. The output of adder 224 is provided to MSE block 236, whichsquares the error and then passes the output signal through a low passfilter. The output of the low pass filter is the MSE 238. MSE 238 is ameasure of the performance of receiver 100, and may be used to tune athreshold for shutting down taps 209 as described in examples below.

Multiple techniques are useful in various examples to shut down filtertaps 209 to reduce current consumption. In one example, the data in thedata path 202 may be zeroed out as shown with the zeros coupled to taps209. An AND gate such as data gates 240A to 240N may be used to zero outthe filter taps 209 that are shut down to reduce current consumption.This technique is called data gating. With data gating, a zero is passedto multipliers 210A to 210N for filter taps 209 that are data gated,which produces an output of zero from multipliers 210A to 210N. Thosefilter taps 209 are therefore shut down via data gating.

Data gating may also be used in LMS block 204 rather than data path 202.The output signal from adder 224 may be zeroed with a data gate 242 fora specific filter tap 209 that is to be shut down. Zeroing out the datain LMS block 204 produces a zero coefficient 234, which shuts down thefilter tap 209.

In another example, clock gating may be used to shut down a filter tap209. A clock signal in LMS block 204 provided to register 232 may beshut down, which causes the coefficient output from LMS block 204 to bezero. The filter taps 209 that are to be shut down may therefore be shutdown using clock gating or data gating.

FIG. 3 is a graph 300 of echo coefficients for 216 echo canceller filtertaps in accordance with various examples. The x-axis indicates thenumber of the filter tap in the echo canceller, such as echo canceller134. The y-axis indicates the value of the echo coefficient. A firstcurve 302 is a graph of a 6-meter Ethernet cable that has two peaks. Afirst peak of curve 302 is near filter tap 20, while a second peak isnear filter tap 70. A second curve 304 is a graph of a 15-meter Ethernetcable, which in this example is composed of a 6-meter cable combinedwith a 9-meter cable. Curve 304 has three peaks, a first peak nearfilter tap 20, a second peak near filter tap 70, and a third peak nearfilter tap 140. The peaks in curves 302 and 304 are the peaks of theecho signal that the echo canceller 134 is configured to cancel.Therefore, in examples herein, filter taps that are near the peaks arekept on so the echo signal may be filtered and removed. Filter taps thatare not near the peaks are shut down to reduce current consumption.

The first peaks in curves 302 and 304 represent the near end echo. Nearend echo is the echo at the receiver from the near end transmittedsignal. The near end echo occurs near filter tap 20 in this example. Thesecond peaks in curves 302 and 304 represent the far end echo. Far endecho is the echo at the receiver from the signal transmitted at the farend. The far end echo occurs near filter tap 70 in this example. The farend echo is delayed behind the near end echo, so it occurs at a laterfilter tap number. The third peak occurs only in curve 304. Curve 304 isa graph of a 15-meter Ethernet cable, composed of a 6-meter cablecombined with a 9-meter cable. The third peak occurs due to reflectionsfrom the connection in the middle of the combined 15-meter cable.

As seen in graph 300, there are 216 filter taps, but only a smallportion of the coefficients are significant. That is, many of thecoefficient values (on the y-axis) are zero or near zero as shown ingraph 300. Therefore, dynamic shutdown of the insignificant filter tapsmay be performed to save power. For example, filter taps with acoefficient value greater than 1 or less than −1 may be consideredsignificant. In conventional systems, after the coefficients of thefilter taps are found, a blind threshold is applied (such as ±1.0). Forcoefficients that are lower than the threshold, the filter tapsassociated with those coefficients are shut down in the conventionalsystem. One way to shut down a filter tap is for the clock or data forthe filter tap to be gated as described above, and then the values ofthose filter taps become zero. Therefore, only the significant filtertaps are left on. The conventional shut down technique may be performedin both echo canceller 134 and DFE 144. However, a limitation of theconventional solution is that if filter taps are shut down using a blindthreshold, the system suffers reduced performance. Reduced performanceoccurs because some coefficients that are significant are neverthelessshut down, as those coefficients are below the threshold (e.g., between1 and −1). A blind threshold, such as the threshold found inconventional systems, leads to reduced performance. If filter taps withsignificant coefficients are shut down, some portion of the echo may notbe cancelled.

In examples herein, the decision to shut down a filter tap is determinedby analyzing not only the filter tap under consideration but also theneighboring (e.g., adjacent) filter taps. As shown in FIG. 2, filtertaps 209 receive output data from shift register 208. In one example,the filter taps are arranged sequentially (209A, 209B, 209C, . . . 209N)in a row, and receive output data from shift register 208 based on theirposition in the row. Neighboring filter taps, adjacent filter taps, orfilter taps next to one another are filter taps that are consecutive inthe row. For example, filter tap 209A is neighboring or adjacent tofilter tap 209B. Filter tap 209B is neighboring or adjacent to bothfilter tap 209A and filter tap 209C. Filter tap 209C is neighboring oradjacent to both filter tap 209B and filter tap 209D. Filter taps thatare within two neighbors of filter tap 209C are filter taps 209A and209B on one side, and filter taps 209D and 209E on the other side. Ifthe echo coefficient of a neighboring filter tap is above a threshold,the filter tap under consideration is kept on. Similarly, if all of apredetermined number of neighboring filter taps are below a threshold,the filter tap is shut down. For example, the nth filter tap is shutdown if neighboring filter taps (n+k to n−k) are below the threshold.The value of k may be determined experimentally. With this technique,filter taps near the peak coefficient values are not shut down, and onlyunwanted filter taps are shut down.

In one example, the value of k is 2, and filter tap 50 is the filter tapunder consideration. If the coefficient value of filter tap 50 is abovethe threshold, filter tap 50 remains on. However, if the coefficientvalue of filter tap 50 is below the threshold, the neighboring filtertaps are considered to determine whether filter tap 50 should be shutdown. With a k of 2, filter taps 48, 49, 51, and 52 are considered.Filter tap 50 is shut down only if the coefficient values of each filtertap 48 through 52 are below the threshold. If any of the coefficientvalues are above the threshold, filter tap 50 is kept on. If all thecoefficient values for filter taps 48 through 52 are below thethreshold, filter tap 50 is shut down. This analysis is performed foreach of the 216 filter taps. Rather than using a blind threshold forshutdown, filter taps that are near filter taps with significantcoefficient values are kept on. In this case, the definition of near isdetermined by the value of k. Larger values of k will result in morefilter taps being kept on compared to smaller values of k. The examplesherein produce lower current consumption while maintaining performanceabove an acceptable threshold, as described below.

For curve 302, filter taps located near filter taps 20 to 30 may be kepton, as those coefficient values are significant or are near othersignificant coefficient values. Likewise, filter taps located nearfilter taps 65 to 75 may be kept on according to examples herein. Forthe 15-meter cable represented by curve 304, filter taps located nearfilter taps 20 to 30 and near filter taps 65 to 75 may be kept on. Also,filter taps near filter taps 140 to 155 may be kept on as well for the15-meter cable.

FIG. 4 is a graph 400 of echo canceller filter taps and echocoefficients in accordance with various examples. The x-axis indicatesthe number of the filter tap in the echo canceller, such as echocanceller 134. The y-axis indicates the value of the echo coefficient. Afirst curve 402 indicates the coefficients for the filter taps with noshutdown of filter taps.

A second curve 404 indicates a conventional system that uses blinddynamic shutdown. For the conventional system, filter taps withcoefficient values below a certain threshold are shut down withoutconsideration of any neighboring filter taps. On curve 404, filter tapsbetween approximately 30 and 40 are shown with a coefficient value ofzero, which means that these filter taps are shut down using the blinddynamic shutdown of the conventional system.

A third curve 406 indicates dynamic shutdown of filter taps usingneighboring filter taps according to an example herein. With curve 406,filter taps are shutdown only if neighboring filter taps are alsounderneath a threshold for shutdown. As seen in curve 406, filter tapsbetween approximately 30 and 40 are still on, whereas those filter tapsare shut down using the blind dynamic shutdown represented by curve 404.Likewise, some filter taps between approximately 145 and 170 are kept onusing the proposed method herein, where those filter taps would be shutdown using the blind dynamic shutdown represented by curve 404.Therefore, in this example, shutting down filter taps by consideringneighboring filter taps leads to more filter taps being kept on than theblind dynamic shutdown of the convention systems.

FIG. 5 is a graph 500 of echo canceller filter taps and echocoefficients in accordance with various examples. The x-axis indicatesthe number of the filter tap in the echo canceller, such as echocanceller 134. The y-axis indicates the value of the echo coefficient.The information in FIG. 5 is the same information conveyed in FIG. 4,but FIG. 5 has a scaled y-axis to better illustrate the differencesbetween the three curves. A first curve 502 indicates the coefficientsfor the filter taps with no shutdown of filter taps. A second curve 504indicates a conventional system that uses blind dynamic shutdown. Athird curve 506 indicates dynamic shutdown of filter taps usingneighboring taps according to an example herein. As seen with curve 502,no shutdown of filter taps leaves many filter taps on even though thesefilter taps have echo coefficient values that are small. With the blindshutdown of curve 504, many filter taps are shut down even though theyhave significant echo coefficient values. As seen with curve 506, thefilter taps that are kept on more closely follow curve 502 than curve504. More filter taps are kept on with curve 506 than curve 504.However, many filter taps that have insignificant values in curve 506are shut down, and those filter taps are shown with an echo coefficientvalue of zero in curve 506.

FIG. 6 is a table 600 of performance results compared to conventionalsystems in accordance with various examples. The conventional approachusing a blind shutdown is compared to the neighbor method according toexamples herein. First, for a cable length of 6 meters, three echocoefficient thresholds are considered: no threshold (all filter tapskept on), a threshold of 1, and a threshold of 2. If all filter taps arekept on, the SNR is 25.1 decibels (dB). If the echo coefficientthreshold is set to 1, the conventional blind shutdown approach resultsin 20 filter taps being kept on and an SNR of 24.9 dB. With a thresholdof 1, the neighbor approach according to examples herein results in 26filter taps being kept on and an SNR of 24.8 dB.

If the echo coefficient threshold is set to 2, the conventional blindshutdown approach results in 12 filter taps being kept on and an SNR of22.9 dB. With a threshold of 2, the neighbor approach according toexamples herein results in 14 filter taps being kept on and an SNR of24.5 dB. With the neighbor approach, two more filter taps are kept on inthis example, and the SNR is higher compared to the conventionalapproach.

Second, for a cable length of 15 meters (a 9-meter cable and a 6-metercable), if all filter taps are kept on, the SNR is 22.9 dB. If the echocoefficient threshold is set to 1, the conventional blind shutdownapproach results in 40 filter taps being kept on and an SNR of 22.3 dB.With a threshold of 1, the neighbor approach according to examplesherein results in 50 filter taps being kept on and an SNR of 22.8 dB.

If the echo coefficient threshold is set to 2 for the 15-meter cable,the conventional blind shutdown approach results in 20 filter taps beingkept on and an SNR of 20.1 dB. With a threshold of 2, the neighborapproach according to examples herein results in 26 filter taps beingkept on and an SNR of 22.1 dB. With the neighbor approach, six morefilter taps are kept on in this example, and the SNR is higher comparedto the conventional approach.

FIG. 7 is a state machine 700 that provides an SNR-based iterativeshutdown method in accordance with various examples. In some examples,one threshold for the echo coefficients that will be shut down is notoptimal for all cable lengths, and may not be optimal for cables formedby multiple cable segments. The SNR at receiver 100 varies with cablelength (e.g. SNR is higher for shorter cable lengths).

In accordance with various examples herein, the threshold may befine-tuned based on a target MSE. The MSE is one measure of theperformance of the system. A high MSE indicates that the error in thesystem is too high, and more filter taps should be kept on to reduce theerror in future iterations. A low MSE indicates that the error in thesystem is low, and some additional filter taps may be turned off toreduce current consumption. Turning off additional filter taps mayincrease the MSE, but if the MSE is below an acceptable level, thattradeoff may be made to reduce current consumption until the MSE reachesa target level. State machine 700 may increase or decrease the thresholdfor shutdown of the echo coefficients in steps. This threshold is tuneduntil the target MSE is reached. At that point, the threshold is set andthe system operates at steady state.

First, state 710 represents the idle state. State 720 is the trainingstep. In state 730A, the dynamic shutdown threshold is determined basedon a target MSE. The threshold is the echo coefficient level that iscompared to the echo coefficients of the filter taps to determine if thefilter taps are significant or not. The MSE is the inverse of the SNR(MSE=1/SNR). State 730B is an example of one approach for determiningthe threshold. First, a target MSE is set, along with a λ error valuethat represents an acceptable margin of error for the MSE. Duringtraining, the MSE of the system is determined (as shown above in FIG.2). If the MSE is below the target MSE minus the λ error value, thethreshold (Thr) is increased by a value of A. In other words, the MSE isbelow the target, and therefore the error in the system is better thanexpected in this example. Because the MSE is below the target, thethreshold for echo coefficients may be increased so fewer filter tapsare kept on during dynamic shutdown (e.g., only taps with higher echocoefficient values above the new threshold are kept on). Fewer filtertaps remaining active will lead to a higher MSE, but as long as the MSEis still below the acceptable range, the tradeoff of fewer filter tapsis made to reduce current consumption while still remaining withinacceptable performance parameters.

On the other hand, if the MSE is above the target MSE plus the λ errorvalue, the threshold (Thr) is decreased by a value of A. Decreasing thethreshold value will activate some filter taps that are currentlyinactive, which will reduce the MSE in the system. In one example, asdescribed above with respect to FIG. 6, a 6-meter cable with a thresholdof 2 results in 14 filter taps being active using the neighbor method.Decreasing the threshold to 1 results in 26 filter taps being on. Theextra 12 filter taps that are activated are the filter taps that haveecho coefficients between 1 and 2 and that satisfy the neighbor methoddescribed herein (e.g., the neighbor values are also considered whendetermining whether to activate a filter tap). In this example, 12additional taps are activated, which reduces the MSE in the system. Theprocess in state 730B repeats until the MSE is within the acceptablerange as determined by the λ error value. If the MSE is within theacceptable range, the state machine 700 proceeds to the steady state atstate 740. In one example, a timeout may also be implemented. If thestate 730B does not produce an MSE within the acceptable range in agiven amount of time, state 730B may time out and proceed to state 740.

Also, the results may change during steady state 740 and fall below anacceptable range. For example, the MSE may be monitored and determinedif it rises above an acceptable predetermined level (e.g., an MSEthreshold). If this occurs, state machine 700 proceeds to state 750.State 750 is a recovery state that occurs responsive to a bit error rate(BER) or an MSE rising above an acceptable level. In the recovery state,all filter taps of the echo canceller 134 and DFE 144 are turned on.Then, the state machine proceeds to state 730A to perform the trainingprocess again as described above.

In some examples herein, the training time for the method described inFIG. 7 may take 30 to 45 milliseconds. However, in some applications thelink-up time is 100 milliseconds, so the increased training time stilloccurs within an acceptable margin of time.

FIG. 8 is a graph 800 of echo canceller filter taps and echocoefficients in accordance with various examples. The x-axis indicatesthe number of the filter tap in the echo canceller, such as echocanceller 134. The y-axis indicates the value of the echo coefficient.

Curve 802 is a curve illustrating the neighboring filter tap shutdownmethod as described herein for a 15-meter cable formed by four cablesegments. Curve 802 has peaks near filter tap 45, filter tap 90, andfilter tap 120. Curve 804 is a curve illustrating the neighboring filtertap shutdown method as described herein for a 15-meter cable formed bytwo cable segments. The peaks of curve 804 are in different filter taplocations compared to the peaks in curve 802. For example, curve 804 haspeaks near filter tap 20, filter tap 70, and filter tap 140.

FIG. 9 is a table 900 of performance results for shutting down filtertaps using the neighbor method in accordance with various examplesherein. Various cable lengths are shown, with single cable lengths ofone meter and six meters. Also shown in table 900 are 15-meter cablelengths composed of two cable segments and four cable segments, and a21-meter cable length composed of four cable segments. In this example,the target SNR is 18 dB. That is, an SNR of 18 dB or greater isconsidered an acceptable performance threshold.

With a one-meter cable length, no shutdown of echo canceller filter tapsprovides an SNR of 26.2 dB, while shutting down echo canceller filtertaps using the method proposed herein results in an SNR of 24.9 dB withonly 8 active filter taps. Therefore, for a cable length of one meter,current consumption may be significantly reduced while still maintainingan SNR well above the target SNR of 18 dB. For a six-meter cable length,no shutdown provides an SNR of 25.3 dB. Shutting down echo cancellerfilter taps using the method proposed herein results in an SNR of 21.1dB with only 8 active filter taps for the six-meter cable.

For the 15-meter cable composed of two cable segments, no shutdownprovides an SNR of 22.9 dB. Shutting down echo canceller filter tapsusing the method proposed herein results in an SNR of 18.7 dB with 12active filter taps for the 15-meter, two-segment cable.

For the 15-meter cable composed of four cable segments, no shutdownprovides an SNR of 22.9 dB. Shutting down echo canceller filter tapsusing the method proposed herein results in an SNR of 18.2 dB with 40active filter taps for the 15-meter, four-segment cable.

Finally, for the 21-meter cable composed of four cable segments, noshutdown provides an SNR of 20.3 dB. Shutting down echo canceller filtertaps using the method proposed herein results in an SNR of 18.1 dB with80 active filter taps for the 21-meter, four-segment cable.

FIG. 10 is a diagram 1000 of a channel length-based shutdown method inaccordance with various examples. In the dynamic shutdown methodsdescribed above, power is saved during steady state operation. Duringtraining, however, all filter taps are on and consuming power. If thecable length is known, some filter taps may be shut down during trainingas well. For example, for a one-meter cable, certain filter taps are notexpected to be significant because there is no far end echo that has tobe cancelled (see, e.g., the description of FIG. 3 above). A 15-metercable length may use active filter taps to handle the far end echo, butthose filter taps are not necessarily used for the one-meter cable.Therefore, certain filter taps may be turned off during training basedon the cable length, to further reduce current consumption.

In one example, the receive gain (AGC) 1002 is useful to determine thefilter tap length. In diagram 1000, AGC 1002 provides a receive gainindex 1004 to a lookup table 1006. Based on the receive gain index 1004,the lookup table 1006 provides a DFE tap length 1008 and an echocanceller tap length 1010. The DFE tap length 1008 and echo cancellertap length 1010 indicate which filter taps may be turned off duringtraining, based on the cable length. For shorter cable lengths, morefilter taps may be turned off.

Table 1050 is an example of the receive gain that is used for differentcable lengths. For small cable lengths, the signal is attenuated by someamount. For example, for a one-meter cable, the signal is attenuated by9 dB. Therefore, the gain is an estimate of the channel length. Thereceiver gain is used in a lookup table to find the cable length, andfrom the cable length a determination is made that the filter tapsbeyond a certain tap value may be shut down. In one example, two lookuptables are used, one for the echo canceller filter taps and one for theDFE filter taps. Based on the receiver gain, the later filter taps maybe shut down during training.

In another example, different cable types may have different lookuptables to determine which filter taps to shut down during training. Forexample, shielded and unshielded cables may have different insertionlosses. Due to the different insertion losses, different amounts of gainmay be useful for these different types of cables of the same length.However, whether the cable is shielded or unshielded, the same filtertaps are kept on for a cable of a given length. Therefore, if one typeof cable has more receiver gain than another type of cable of the samelength, the lookup tables should reflect that the same number of filtertaps should remain on for each cable type, even though the receiver gainis different.

FIG. 11 is a flow diagram of a method for reducing power consumption inan Ethernet receiver in accordance with various examples. The steps ofmethod 1100 may be performed in any suitable order. The hardwarecomponents described above with respect to FIGS. 1 and 2 may performmethod 1100 in one example.

Method 1100 begins at 1110, where a filter receives an input signal,where the filter includes a plurality of filter taps, and where each ofa first filter tap and a second filter tap has a weighting coefficient.As described above in the description regarding FIG. 2, in one example afilter within echo canceller 134 receives an echo signal and filters theecho signal using filter taps with weighting coefficients.

Method 1100 continues at 1120, where the first filter tap is shut downbased on the weighting coefficient of the first filter tap being below athreshold and the weighting coefficient of the second filter tap beingbelow the threshold, where the second filter tap is next to the firstfilter tap. As described above, shutting down filter taps by consideringwhether neighboring filter taps are below a threshold producesacceptable results (such as acceptable SNR) while reducing current andpower consumption.

The term “couple” is used throughout the specification. The term maycover connections, communications, or signal paths that enable afunctional relationship consistent with this description. For example,if device A generates a signal to control device B to perform an action,in a first example device A is coupled to device B, or in a secondexample device A is coupled to device B through intervening component Cif intervening component C does not substantially alter the functionalrelationship between device A and device B such that device B iscontrolled by device A via the control signal generated by device A.

A device that is “configured to” perform a task or function may beconfigured (e.g., programmed and/or hardwired) at a time ofmanufacturing by a manufacturer to perform the function and/or may beconfigurable (or re-configurable) by a user after manufacturing toperform the function and/or other additional or alternative functions.The configuring may be through firmware and/or software programming ofthe device, through a construction and/or layout of hardware componentsand interconnections of the device, or a combination thereof.

As used herein, the terms “terminal,” “node,” “interconnection” and“pin” are used interchangeably. Unless specifically stated to thecontrary, these terms are generally used to mean an interconnectionbetween or a terminus of a device element, a circuit element, anintegrated circuit, a device, or other electronics or semiconductorcomponent.

Unless otherwise stated, “about,” “approximately,” or “substantially”preceding a value means +/−10 percent of the stated value. Modificationsare possible in the described examples, and other examples are possiblewithin the scope of the claims.

What is claimed is:
 1. A system, comprising: a filter configured toreceive an input signal, the filter having a first tap, a second tap anda third tap and each first tap, second tap and third tap has a weightingcoefficient and a data gate; and wherein the data gate is configured toshut down the first filter tap responsive to the weighting coefficientsof the first filter tap, the second filter tap, and the third filter tapeach being below a threshold, and wherein the second filter tap and thethird filter tap are each next to the first filter tap.
 2. The system ofclaim 1, wherein the filter is within an echo canceller in an Ethernetreceiver.
 3. The system of claim 1, wherein the filter is within adecision feedback equalizer in an Ethernet receiver.
 4. The system ofclaim 1, wherein the threshold is based at least in part on a signal tonoise ratio of an Ethernet receiver.
 5. The system of claim 1, whereinthe data gate is configured to shut down the first filter tap responsiveto the weighting coefficients of a fourth filter tap and a fifth filtertap each being below the threshold, wherein the fourth filter tap isnext to the second filter tap, and the fifth filter tap is next to thethird filter tap.
 6. The system of claim 1, wherein the threshold isbased at least in part on a channel length of an Ethernet system.
 7. Thesystem of claim 1, wherein the data gate is configured to shut down thefirst filter tap by zeroing the weighting coefficient of the firstfilter tap.
 8. A method, comprising: receiving an input signal at afilter, wherein the filter includes a plurality of filter taps, andwherein each of a first filter tap and a second filter tap has aweighting coefficient; and shutting down the first filter tap based onthe weighting coefficient of the first filter tap being below athreshold and the weighting coefficient of the second filter tap beingbelow the threshold, wherein the second filter tap is next to the firstfilter tap.
 9. The method of claim 8, further comprising: shutting downthe first filter tap by clock gating the weighting coefficient of thefirst filter tap.
 10. The method of claim 8, further comprising:shutting down the first filter tap by data gating the weightingcoefficient of the first filter tap.
 11. The method of claim 8, furthercomprising: shutting down the first filter tap based on the weightingcoefficient of a third filter tap adjacent to the first filter tap beingbelow the threshold.
 12. The method of claim 8, wherein the threshold isbased at least in part on a signal to noise ratio of an Ethernetreceiver.
 13. The method of claim 8, wherein the threshold is based atleast in part on a channel length of an Ethernet system.
 14. The methodof claim 8, wherein the filter is within an echo canceller in anEthernet receiver.
 15. A method, comprising: determining a mean squareerror (MSE) for a signal in an Ethernet receiver; comparing the MSE to atarget MSE; changing a threshold for shutting down a filter tapresponsive to the MSE being above or below the target MSE and an errorvalue; and setting the threshold for shutting down the filter tapresponsive to the MSE being above the target MSE minus the error valueor below the target MSE plus the error value.
 16. The method of claim15, wherein the target MSE is based at least in part on a target signalto noise ratio of the Ethernet receiver.
 17. The method of claim 15,wherein the target MSE is based at least in part on a channel length ofan Ethernet system.
 18. The method of claim 15, further comprising:monitoring the MSE of the signal; and turning on all filter tapsresponsive to the MSE of the signal rising above an MSE threshold. 19.The method of claim 15, further comprising: shutting down the filter tapby data gating a weighting coefficient of the filter tap.
 20. The methodof claim 15, wherein the filter tap is a first filter tap, and whereinthe first filter tap is shut down based on a weighting coefficient ofthe first filter tap and a weighting coefficient of a second filter tapbeing below the threshold, wherein the second filter tap is adjacent tothe first filter tap.